In recent years, global warming and environmental destruction have become an international problem, and from the viewpoint of environmental protection, various emission regulations have been set in each country. Among them, discharge of volatile organic compounds (VOC) such as organic solvents into the atmosphere is a serious problem, and de-VOC movement is being advanced by VOC emission regulations.
Also in the paint industry, from the viewpoint of de-VOC movement, powder coating materials have now been widely used. Powder coating materials have no or little content of organic solvents and thus are easy in management of the exhaust gas or solvent waste during their use, and further, it is even possible to recover and reuse the coating materials themselves, and thus, their environmental impact is very low.
On the other hand, in recent years, in various fields such as construction, automobiles, etc., there is an increasing demand for a coating film exhibiting a metallic hue (luster color). In order to form a coating film with a luster color, a powder coating material containing a luster pigment such as aluminum powder or mica powder is used.
As such a powder coating material, a powder coating material made of a powder coating resin having a luster pigment adhered on its surface is known. As a method of letting the luster pigment be adhered to the surface of the powder coating resin, Patent Document 1 discloses a method, as an embodiment of so-called dry blending method, wherein a powder resin and an aluminum powder are mixed at from 50 to 60° C., to soften the surface of the powder resin, thereby to let the aluminum powder be adhered to the powder resin (paragraphs 0062, etc.).